Earth boring bits of the type used in drilling oil or gas wells are subjected to severe and destructive conditions of stress, shock, abrasion, corrosion and temperature. It has been reported that drill bits can be subjected to 40,000-50,000 pounds of drilling pressure. A typical such drill bit comprises three roller cutters or cones with external cutting teeth mounted for rotation on a stationary journal or bearing shaft. In operation, the bit is threaded onto a drill string or drill pipe and drilling fluid or mud is injected into the well bore through the pipe to flush out the rock chips and other detritus as they are formed. Normally, a drill bit of this type will be operated until the cutting teeth or the bearings supporting the cones on the shaft become excessively worn. Thus, the preservation of the bearing surfaces between the cones and their bearing shafts is critical to the operating lifetime of an earth boring bit.
As a general rule, the earth boring drill bit is provided with means for lubricating the bearings thereof. However, great care must be taken to prevent the loss of the lubricant or the entrance of abrasive rock fragments or corrosive material into the bearings. To this end, there have heretofore been provided numerous sealing systems designed to withstand the destructive operating conditions and the complex movements of the cutter cones which include wobbling and axial movement as well as rotation about the axis of the bearing shaft.
The criticality of the sealing systems and the steps heretofore taken in an effort to provide even more efficient and durable systems may best be appreciated by referring to U.S. Pat. No. 4,516,641 to Burr, which traces the evolution of the cylindrical journal or shaft provided with a single seal comprising pairs of opposed resilient rings and rigid rings positioned in a seal groove between the shaft and cutter cone. That reference also refers to and describes the teachings of a number of earlier earth boring bits U.S. patents, including U.S. Pat. No. 930,759 to Hughes; U.S. Pat. No. 3,075,781 to Atkinson et al U.S. Pat. No. 3,397,928 to Galle; U.S. Pat. No. 3,180,648 to Kupfert; U.S. Pat. No. 3,216,513 to Robbins; U.S. Pat. No. 3,452,995 to Engelking; and U.S. Pat. No. 3,761,145 to Schumacher, Jr.
In addition to the above listed patents, applicant is aware of U.S. Pat. No. 3,656,764 to Robinson, showing a generally cylindrical bearing shaft with single seal in a groove comprising a pair of compressible rings and a metal ring; U.S. Pat. No. 4,394,020 to Oelke, showing a generally cylindrical bearing shaft with single seal in a groove comprising a pair of compressible rings and a metal ring; and U.S. Pat. No. 4,632,401 to Kar et al., which teaches a generally cylindrical bearing shaft and a single belleville seal comprising metal encased in an elastomeric material.
It is desirable that the earth boring drill bits be operated for the longest possible time between bit changes. However, the cited prior patents illustrate that the search for a more durable bit and more efficient sealing system therefor continues unabated.